The present invention generally relates to low bit rate transmissions and, more particularly, to a method and apparatus for providing format conversion of video to enable low bit rate compression of non-progressive video.
Video fields are sometimes interlaced to enable serial video bit streams to be sent over networks. Interlacing includes sending alternating fields of video successively over a link. Video streams may be identified as progressive or non-progressive. Progressive video includes pairs of successive fields where there is no object motion between pairs of successive fields. Non-progressive video can include fields where there is object motion between successive pairs of fields. Progressive frames can easily be format converted; however, format converting non-progressive video does not enjoy the same capability. Instead, non-progressive video is much more difficult to format convert without significant loss in vertical resolution.
One approach to this downconverting is to use intra-field interpolation to convert 240-line incoming fields to 120-line fields. The resulting 240 interlaced (240i) video is compressed, transmitted, and decompressed. The 240i video is then intra-field converted by vertical interpolation to 240-line fields of a 480i signal and displayed. The vertical resolution suffers, especially in comparison to 240 progressive picture processing. Diagonal edges of moving objects are jagged, as well.
Therefore, a need exists for a method and system, in which non-progressive video is downconverted to lower picture resolution for acceptable compression to low bit rate video. A further need exists for adequate picture quality after upconverting the transferred low bit rate video.
A method for format conversion includes providing a first interlaced video signal including non-progressive video of a first resolution, downconverting fields of the first resolution to fields of a second resolution, and combining and interlacing the fields at a third resolution. The video signal is transmitted at the third resolution. The video signal of the third resolution is deinterlaced to form a progressive format video. The progressive format video is converted to the first non-progressive resolution by alternately adjusting position of the progressive format of the third resolution up and down to make upper and lower fields, respectively, of the first resolution for display.
In other embodiments, the step of deinterlacing the non-progressive video signal to a progressive format having the first resolution may be included. A jagged diagonal reduction method may be employed to perform deinterlacing.
A system for format conversion includes a conversion device, which deinterlaces a non-progressive interlaced video signal having a first resolution to a progressive format having the same resolution. The conversion device downconverts the progressive format to a second resolution and combines and interlaces fields of the second resolution to provide frames at a third resolution. A transmission link is coupled to the conversion device for transmitting the video signal at the third resolution. A reconversion device is coupled to the output of the transmission link. The reconversion device deinterlaces the video stream of the third resolution as a progressive format video and converts the progressive format video to alternating upper field lines and lower field lines for display at the first resolution.